Method of sweetening petroleum distillates



Aug. 17, 1937.

C. E. DOLBEAR METHOD OF SWEETENING PETROLEUM DISTILLATES Filed Dec. 6, 1954 INVENTOR.

BY /64/6 @A CL-uacby/ ATTORNEYS.

Patented Aug. 17, 1937 UITE STTS iCE METHOD OF SWEETENING PETROLEUM DISTILLATES Application December 6, 1934, Serial No. 756,209

Claims.

This invention relates toi a method of sweetening petroleum distillates, and more particularly gasoline and other light petroleum distillates, to render the same sweet-odored, non-corrosive,

5 sweet to the so-called doctor test, and of low gum content.

The principal object of the invention is to provide a novel, effective and economical method of sweetening sour petroleum distillates, and of de-gumming either a sweet or sour distillate,

which is free from certain disadvantages attendant upon methods heretofore commonly used for this purpose, and which can be practiced at a lower cost of operation.

A so-call-ed sour distillate derives its corrosive and bad-odored characteristics chiefly from the presence therein of certain organic sulphur-bearing compounds such as mercaptans, and the purpose of the treatment herein described, as in other sweetening processes, is to cause oxidation of such mercaptans and allied sulphur compounds to form alkyldisulphides or other substances which are substantially noncorrosive to metals and either odorless or 0f inoffensive odor.

One of the sweetening methods now widely employed in the art is the so-called doctor treatment, which consists in intimately contacting the distillate with an aqueous solution of caustic sodium plumbite and adding elemental sulphur, and afterward separating the aqueous solution and any precipitated solids from the distillate. Another method in common use consists in intimately contacting the distillate with an aqueous solution of sodium hypochlorite and then separating the solution from the treated distillate. Both of these methods involve agitation of the distillate with an aqueous solution which generally causes emulsication of a portion of the distillate 4,0 with the solution and thus results in a loss of distillate. Also, in the` case of the doctor treatment a further loss is occasioned due to the adherence of some of the distillate to the precipitated solids. Furthermore, both of these methods are rather costly, particularly on account of the relatively high consumption of reagents employed therein.

A particular object of the present invention is to provide a treating process for sweetening and de-gumming petroleum distillates, in which the cost of reagents consumed is very much less than in the processes above mentioned, and in l which there is little or no loss of distillate attendant upon the sweetening treatment.

The process of the present invention, while speciiically identied as a sweetening process is also, as above set forth, useful in de-gumming petroleum distillates, and the practice of the process either for sweetening a sour distillate, degurnming a sweet distillate, or coincidentally degumming and sweetening a sour distillate, is within the contemplation of the invention.

I have found that if a petroleum distillate containing mercaptans or other objectionable sulphur-bearing organic compounds is subjected, at a suitable temperature, to contact with air in the presence of a solid oxidation catalyst at a suitable temperature in the substantial absence of water, such mercaptans or other objectionable compounds are readily oxidized to alkyldisul- 15 phides or other non-corrosive compounds having no offensive odor, and the distillate is thus sweet to the doctor test, of sweet odor, non-corrosive, and of lowered gum content. The effectiveness of the contact treatment with the oxidation cata- 20 lyst and air extends from temperatures as low as F. to as high as 600 F., and, regardless of the temperature at which the contact is carried out, I have found that the distillate may be caused to contact the catalyst in the presence of air or 25 other convenient source of oxygen, and a very high degree of sweetening and de-gumming obtained, without damage to or apparent change in the nature of the catalyst itself. The air and distillate should be brought into intimate con- 30 tact with one another in the presence of the solid oxidation catalyst, and the latter should be in such condition as to provide a relatively large surface of contact between said catalyst and the air and distillate. 35

lIhe oxidation of the objectionable sulphur compounds may be carried out by simply shaking the sour distillate with the oxidation catalyst in pulverulent or divided condition, in an open Vessel in such manner as to provide access of air, 40 at ordinary atmospheric temperature. However, under these conditions the oxidation generally progresses rather slowly, and I have found that the reaction may be accelerated by the use of a somewhat elevated temperature and by providing more intimate contact between the air and distillate in the presence of the catalyst. Thus, the invention may advantageously be practiced by simultaneously passing the distillate and air 5 through and in intimate contact with a body of the oxidation catalyst in granular or divided condition at a temperature above atmospheric, although satisfactory results may also be obtained by passing air in divided condition through a 55 body ofheated distillate containing nely divided catalyst in suspension.

The distillate may be subjected to the treatment herein described, in either liquid phase or vapor phase, and either at atmospheric pressure or temperature or any other desired higher or lower pressure, it being understood that the pressure or temperature may be 'so selected as to maintain the distillate largely or wholly in the desired liquid or vapor state at the particular temperature employed. However, it will be further understood that it is not necessary that the distillate may be maintained wholly in either the liquid or vapor state during treatment, as the temperature and pressure conditions may be such as to maintain certain constituents thereof partially or wholly in liquid phase and other constituents thereof largely or wholly in vapor phase.

As the temperature of treatment is increased, there is an increasing tendency for the oxygen of the air, in the presence of the oxidation catalyst, to combine or react with constituents of the distillate other than those producing corro-- siveness or oensive odor. Oxidation of these other constituents should be avoided as far as possible, not only because of the loss of valuable combustible constituents which may result therefrom, but also because the products thus formed are apt 4to form gums or to cause the distillate to become darker in color upon standing or exposure to light. For the above reasons, I prefer to closely control the amount of air employe-d at higher temperatures. The highest temperature which may advantageously be employed is different with different distillates, depending upon the degree of unsaturation and other properites of the constituents thereof, and upon the previous treatment to which the distillate may have been subjected. Also the maximum permissible temperature may also vary with the pressure employed and other reaction conditions, and particularly with the specific oxidation catalyst employed. Consequently, it is impossible to definitely state the preferred or permissible range of temperatures which should or may in general be employed. In general, however, for any particular distillate, using a certain oxidation catalyst, and with a xed set of conditions other than temperature, there is considerable range of temperature within which oxidation of the objectionable inercaptans and the like may be readily effected without causing undue oxidation of other constituents, and in any specific instance this temperature range, or the optimum temperature within said range, may readily be determined by experiment.

I have found that sodium ferrite is a highly active oxidation catalyst for the purposes of this invention, although in its place I may also use any other solid oxidation catalyst, and more particularly, a solid catalyst capable of catalytioally promoting the oxidation of mercaptans and the like by the oxygen of the air, at a temperature somewhat below that at which such catalyst tends to cause undue oxidation of other nonobjectionable constituents of the particular distillate to be treated. As examples of other catalysts which may be employed for this purpose, with varying success, I may mention soda lime, caustic soda, and metallic oxides such as red or black iron oxide, molybdic oxide, Zinc oxide and the like, suitably activated as by calcination.

So far as I have been able to detect, sodium ferrite is not subject to catalyst poisoning by even extremely sour gasoline or other distillate, as

long as at least a small amount of air is used in the treatment contact, nor does there seem to be any tendency for the accumulation of impurities or reaction products due to the sulphur compounds in the oil on the surfaces thereof or in a bed of this catalyst. The catalytic action thereof for the purpose of this invention appears to be substantially unimpaired even after use in the treatment of large quantities of distillate. Consequently, the consumption of this catalyst is almost negligible. There is a distinct reduction in the gum content of the distillate in passing through the bed of reagent, which is quite presumably due to absorption or adsorption by the catalyst, in which case the catalyst eventually will become clogged, and may be revivifled or cleansed by heating in the presence of air or by passing super-heated steam in Contact therewith, or by treatment with a suitable solvent such as acetone.

The accompanying drawing illustrates, somewhat schematically, a suitable form of apparatus for use in carrying out this invention in the treatment of a liquid distillate. Said apparatus comprises a closed reaction chamber I provided with suitable heating means such as a jacket 2 through which steam, hot water, or other heating medium may be circulated through connections 3 and ll, whereby the contents of said chamber may be kept at any desired temperature. Said chamber is also provided with a pervious false bottom such as screen 5 supported on perforated plate 6, said screen being of sufiiciently ne mesh toi support the pervious bed or body of granular or divided solid catalyst shown at 1, while permitting free flow of fluid therethrough. In order to permit introduction and removal of said catalyst, I have shown chamber I as provided with a removably secured tighttting charging door 8 at its upper end and with a removably secured tight-fitting discharge door 9 just above the screen 5, but it will be understood that any other suitable means may be provided for this purpose. The construction of the reaction chamber should, of course, be such as to withstand any superatmospheric or sub-atmospheric pressure which it is desired to maintain therein, and the outer walls thereof may be heat-insulated, if desired.

Means such as a perforated pipe coil Il are provided in the upper portion of chamber I for distributing liquid distillate over the upper surface of the body of catalyst, said distributing means being connected to suitable distillate supply means IZ. Means such as pipe I3 are also pro-vided for supplying air to said chamber, preferably into the upper portion thereof above the body of catalyst.

From the bottom olf chamber I, an outlet pipe IIS leads preferably to the coil I'I of condenser I8, through which water or other cooling medium is circulated through connections I9 and 2l. The outlet end olf condenser coil I'I is Iconnected by pipe 22 to a separating chamber 23, in which excess air may be separated from the treated distillate, said separating chamber being provided with a liquid outlet pipe 24 at its lower end and with an air outlet pipe 25 communicating with the upper portion thereof above the liquid level such as shown at 2t, which may be maintained, for example, by means of a liquid trap 2l.

In operation of this apparatus, the chamber I is charged with a suitable quantity of sodium ferrite or other oxidation catalyst in granular condition, such as a minus 8 mesh product, so as to provide a catalyst bed 'l of suicient depth to effect the desired sweetening action at the rate of distillate flow to be employed, and said catalyst may be heated to any desired temperature. The gasoline or other distillate to be treated, icontaining mercaptans or other allied compounds, is then introduced through distributing means li,

`While air is simultaneously introduced through pipe I3. Either the distillate or the air, or both, may advantageously be pre-heated to approximately the desired reaction temperature be-fore introduction thereo-f into the reaction chamber, although such pre-heating is not necessary, as the entire heating may be accomplished within the reaction cham-ber.

The distillate and air then pass concurrently down through and in intimate contact with the bed of catalyst, resulting in oxidation of the mercaptans or other allied compounds, as above set forth. The rate of flow of liquid should be less than the rate at which it would flow as a continuous liquid stream through the voids of the pervious catalyst, and I prefer to so adjust the rate of supply of the distillate that the liquid flows in a relatively thin film over the surfaces of the particles of the catalyst while leaving the voids therebeween sufciently open to permit free ow ofi -air therethrough, thus providing the most intimate contact between the distillate, air, and catalyst. At the rate of liquid flow which is thus preferably maintained, I have found that when using sodium ferrite or other highly active oxidation catalysts, the desired oxidation reaction may be completed by passage of the distillate and air through a catalyst bed having only a relatively small depth, for example, a depth of only a few inches to a few feet. Therefore, in order to obtain the highest efficiency in operation, I prefer to employ a catalyst bed of only about the limited depth necessary to effect the desired reaction at the preferred rate of liquid ow, as above set forth, and to make the horizontal dimensions of said bed suiiicient to handle y the desired volume of distillate at that rate of liolvf.

The rate of introduction of air is preferably maintained somewhat in excess of that required to effect the desired oxidation of objectionable constituents, in order to provide effective contact of oxygen with the distillate throughout the entire depth of the catalyst bed.

Any consituents of they distillate which are vaporized u -pon heating to the reaction temperature employ ed, either before or after introduction into the reaction chamber, also pass with the air through and in intimate contact with the bed of catalyst, s that they are also subjected to the above-described siweetening reaction. It will be understood that the portion of distillate thus vaporized may include not only constituents whose boiling point is actually below the reaction temperature employed, but also higher boiling constituents which are taken up by the air stream due to their vapor pressure at said temperature.

The sweetened liquid and vapor constituents of the distillate, together with excess air, pass from the bed of catalyst into the space below the false bottom ot the reaction chamber, whence they are conducted through pipe lli -to condenser coil I1, which is maintained at a sufficiently low temperature to cause condensation of the major portion of the distillate vapors, by passage of cold water or other cooling medium around said Coil. The liquid distillate and excess air then pass into separating chamber 23, wherein the liquid is separated from the excess air. The sweetened liquid distillate is delivered through pipe 24 and trap 2 to storage, while the excess air passes out through pipe 25 and may, if -del sired, be subjected to further treatment for, recovering any remaining distillate vapors therefrom.

At temperatures suiiicie-ntly high as to cause the distillate to be substantially entirely in vapor phase, for example in the treatment of gasoline at a temperature of 460 F. or higher, l prefer to admit very little air to the reaction chamber, whereby the gum content of the distillate is `not caused to increase, and at the same time a very effective sweetening of the stock obtained.

By subjecting sour gasoline and other `distillates to treatment substantially as above described, I have obtained products which are free from offensive odor, non-corrosive, and sweet to` the doctor test, and in which the gum content is only a small fraction of that present in the distillate before treatment. For example, a very sour cracked gasoline showing 38 milligrams per 100 cc. by copper dish test was subjected to treatment by the pres-ent process, using sodium` ferrite as the oxidation catalyst, at 145 F. The treated gasoline showed only 0.75 mg. by the copper dish test and was doctor sweet. The same gasoline treated at 175 F. was also found to be doctor sweet and showed 3.0 mg. by the copper dish test. Both of these products showed absolutely no corrosion in the copper dish tests.

It will be understood that the above-described form of apparatus is but one of many arrangements that may be employed for the: sweetening and de-gumming of distillate by the method of my invention, and is by no means to be understood as limiting or dening the scope of this invention. In general, I may use any form of apparatus in which the distillate is brought into intimate contact with an oxidation catalyst at suitable temperature and pressure, in the presence of air.

As above pointed out, the treatment may be applied to a sour distillate maintained largely or wholly in vapor phase during the oxidation reaction, by merely heating the same to a suicient temperature, or by so reducing the pressure at the particular temperature to be employed, as to convert said distillate to the vapor state, either before or after introduction into the reaction chamber, and subsequently cooling they vapor leaving said reaction chamber to cause condensation of the sweetened distillate. This embodiment of the invention may be practiced, for example, in an apparatus comparable to that above described, With only minor and obvious changes such as to provide for passage of the distillate through the reaction chamber in vapor instead of liquid state.

The process herein described is not subject to the above-mentioned loss of distillate which occurs in the usual sweetening processes now in common use. Due to the absence of any liquid other than the distillate itself, that is, particularly due to the non-aqueous nature of the contact treatment, no emulsions are formed, and since no precipitate or solid matter is formed in the distillate there can be no loss through retention of any part of the distillate by such a precipitate or solid body. The only loss that can occur is through incomplete stripping of distillate vapors from the excess air, and this loss can be made negligible by keeping the proportion of excess air small and by effecting recovery of a high proportion of such vapors therefrom in any Well-known manner.

It is the oxygen of the air, in the presence of the catalyst, which causes the above-described sweetening reaction to take place and, while air is probably the only practical source of oxygen for use in commercial operation, it will be understood that oxygen gas, or other gas containing oxygen, could be used without departing from the spirit of this invention or from the intended scope of the claims which form a part of this specication.

I claim:

1. The method of treating light petroleum distillates which comprises: passing such a distillate in liquid state downwardly through a pervious bed 0f granular sodium ferrite at such rate as to cause the liquid distillate to flow in a film over the surfaces of said Vsodium ferrite while leaving the voids of said bed open to flow of air, and simultaneously passing air through said bed in intimate contact with said lm of liquid distillate.

2. The method set forth in claim 1, in which such distillate comprises one containing inoffensive unsaturated compounds, the Contact treatment obtained through said passage of distillate and air through said bed being carried out at a temperature above atmospheric temperature but below that at which said air tends to cause extensive oxidation of said inoffensive unsaturated compounds.

3. The method of treating light petroleum distillates which comprises bringing such a distillate into intimate Contact with air and sodium ferrite.

4. The method of treating light petroleum distillates containing inoffensive unsaturated compounds which comprises bringing such a distillate into intimate Contact with air and with sodium ferrite in divided condition, at a temperature above atmospheric temperature but below that at which said air tends to cause extensive oxidation of said inoffensive unsaturated compounds.

5, The method of treating"doctor sour gasoline to render the same Ydoctor sweet which comprises bringing the sour gasoline into intimate contact with air and sodium ferrite, to make said gasoline "doctor sweet, and separating the sweetened gasoline from excess air and from said sodium ferrite.

CLINTON E. DOLBEAR. 

